COLE-PARMER LABORATORY CHLORIDE ION ELECTRODE INSTRUCTION MANUAL

Transcription

1 COLE-PARMER LABORATORY CHLORIDE ION ELECTRODE INSTRUCTION MANUAL Cole-Parmer Instrument Company (800) Fax:(847) East Bunker Court, Vernon Hills, Illinois

2 TABLE OF CONTENTS General Instructions...3 introduction...3 required equipment...3 required solutions...3 General Preparation...4 electrode preparation...4 electrode slope check (with ph/mv meter)...4 electrode slope check (with ion meter)...5 Measurement...5 measuring hints...5 sample requirements...6 units of measurement...6 Measurement Procedure...6 direct measurement...6 direct measurement of chloride (using a ph/mv meter)...6 direct measurement of chloride (using an ion meter)...8 low level chloride determination (using a ph/mv meter)...9 low level chloride determination (using an ion meter)...10 Electrode Characteristics...10 reproducibility...10 interferences...11 removal of various interferences with cisa...11 complexation...12 temperature influences...12 electrode response...13 limits of detection...14 ph effects...14 electrode life...15 electrode storage...15 Electrode Theory...15 electrode operation...15 Troubleshooting Guide...16 Troubleshooting Hints...19 Electrode Specifications...21 Ordering Information

3 COLE-PARMER CHLORIDE ION ELECTRODES INSTRUCTION MANUAL GENERAL INSTRUCTIONS Introduction The Cole-Parmer Chloride Ion Electrodes are used to quickly, simply, accurately, and economically measure chloride ions in aqueous solutions. Required Equipment 1. A ph/mv meter or an ion meter, either line operated or portable. 2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the meter in the mv mode. 3. A magnetic stirrer. 4. The Cole-Parmer Chloride Ion Combination Glass Electrode, Cat. No , or the Cole-Parmer Chloride Ion Combination Epoxy Electrode, Cat No Polishing Paper to polish dirty or etched electrode membranes. Required Solutions 1. Deionized or distilled water for solution and standard preparation. 2. Cole-Parmer Ionic Strength Adjuster (ISA), 5M NaNO 3, Cat. No To prepare this solution from your own laboratory stock, half fill a 1000 ml volumetric flask with distilled water and add 425 grams of reagent-grade sodium nitrate, NaNO 3. Swirl the flask to dissolve the solid. Fill the flask to the mark with distilled water, cap, and invert the flask several times to mix the contents. ISA is added at the rate of 2 ml of ISA to each 100 ml of standard or sample to adjust the ionic strength to about 0.1M. 3. Cole-Parmer Electrode Filling Solution, 1M KNO 3, Cat. No , for both the and chloride combination electrodes. 4. Cole-Parmer Chloride Standard, 0.1M NaCl, Cat. No To prepare this solution from your own laboratory stock, add 5.84 grams of reagent-grade sodium chloride, NaCl, to a one liter volumetric flask about half-full of distilled water. Swirl the flask to dissolve the solid. Fill to the mark with distilled water, cap, and upend the flask several times to mix the solution. 3

4 5. Cole-Parmer Chloride Standard, 1000 ppm Cl -1, Cat. No To prepare this solution from your own laboratory stock, add 1.65 grams of reagent-grade sodium chloride, NaCl, to a one liter volumetric flask about half-full of distilled water. Swirl the flask to dissolve the solid. Fill to the mark with distilled water, cap, and upend the flask several times to mix the solution. 6. Cole-Parmer Chloride Standard, 100 ppm Cl -1. To prepare this solution from your own laboratory stock, add grams of reagent-grade sodium chloride, NaCl, to a one liter volumetric flask about half-full of distilled water. Swirl the flask to dissolve the solid. Fill to the mark with distilled water, cap, and upend the flask several times to mix the solution. GENERAL PREPARATION Electrode Preparation Remove the rubber cap covering the electrode tip and the rubber insert covering the filling hole of the reference electrode. Fill the combination electrode with the filling solution shipped with the electrode to a level just below the fill hole. No preparation is required with a sealed reference electrode. Connect the electrode to the proper terminals of the meter as recommended by the meter manufacturer. Electrode Slope Check (with ph/mv meter) (check electrode each day) 1. To a 150 ml beaker, add 100 ml of distilled water and 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mv mode, lower the electrode tips into the solution. 2. Using a pipet, add 1 ml of 0.1M or 1000 ppm chloride standard to the beaker. When the reading has stabilized, record the millivolt reading. 3. Using a pipet, add 10 ml of the same chloride standard used above to the beaker. When the reading has stabilized, record the millivolt reading. 4. Determine the difference between the two readings. A difference of 56 ± 2 mv indicates correct electrode operation, assuming the solution temperature is between 20 and 25 C. See the TROUBLESHOOTING section if the potential change is not within this range. Slope is defined as the change in potential observed when the concentration changes by a factor of 10. 4

5 Electrode Slope Check (with ion meter) (check electrode each day) 1. Prepare standard chloride solutions whose concentrations vary by tenfold. Use either the 0.1M or 1000 ppm chloride standard. Use the serial dilution method for this preparation. 2. To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip into the solution. Assure that the meter is in the concentration mode. 3. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer s instructions. 4. Rinse the electrode with distilled water and blot dry. 5. To another 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip into the solution. 6. Adjust the meter to the concentration of the standard and fix the value in the memory. 7. Read the electrode slope according to the meter manufacturer s instructions. Correct electrode operation is indicated by a slope of %. See the TROUBLESHOOTING section if the slope is not within this range. MEASUREMENT Measuring Hints All samples and standards should be at the same temperature for precise measurement. A difference of 1 degree C in temperature will result in about a 2% measurement error. Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can generate sufficient heat to change the solution temperature. To counteract this effect, place a piece of insulating material, such as styrofoam sheet, between the stirrer and beaker. Always rinse the electrode with distilled water and blot dry between measurements. Use a clean, dry tissue to prevent cross-contamination. For samples with high ionic strength, prepare standards whose composition is similar to the sample. Always check to see that the membrane is free from air bubbles after immersion into the standard or sample. 5

6 Sample Requirements All samples must be aqueous and not contain organics which can dissolve the epoxy electrode body and/or the cement bonding the sensing crystal to the electrode body. Infrequent measurements in solutions containing methanol, ethanol, benzene, and acetonitrile are permitted. Highly polar solvents slowly attack the electrode. Please check with Cole-Parmer Instrument Company before using the electrode in other organic solvents. The temperature of the standard solutions and of the sample solutions should be the same and below 50 C. Interferences should be absent. If they are present, use the procedures found in the Interferences and Electrode Response sections to remove them. The ph range for the chloride ion electrode is Neutralize samples outside this range with acid or base to bring them in range. Units of Measurement Chloride concentrations are measured in units of parts per million, equivalents per liter, moles per liter, or any other convenient concentration unit. Table 1 indicates some of the concentration units. TABLE 1: Concentration Unit Conversion Factors MEASUREMENT PROCEDURE Direct Measurement ppm Cl -1 moles/liter Cl x x x 10-4 Direct measurement is a simple procedure for measuring a large number of samples. A single meter reading is all that is required for each sample. The ionic strength of samples and standards should be made the same by adjustment with ISA for all chloride solution. The temperature of both sample solution and of standard solutions should be the same. Direct Measurement of Chloride (using a ph/mv meter) 1. By serial dilution of the 0.1M or 1000 ppm standards, prepare 10-2, 10-3, and 10-4 M or 100 and 10 ppm chloride standards. Add 2 ml of ISA per 100 ml of standard. Prepare standards with a composition similar to the samples if the samples have an ionic strength above 0.1M. 6

7 2. Place the most dilute solution (1.0 x 10-4 M or 10 ppm) on the magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mv mode, lower the electrode tip into the solution. When the reading has stabilized, record the mv reading. 3. Place the mid-range solution (1.0 x 10-3 M or 100 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrodes with distilled water, blot dry and immerse the electrode tip in the solution. When the reading has stabilized, record the mv reading. 4. Place the most concentrated solution (1.0 x 10-2 M or 1000 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrodes with distilled water, blot dry and immerse the electrode tip in the solution. When the reading has stabilized, record the mv reading. 5. Using the semi-logarithmic graph paper, plot the mv reading (linear axis) against the concentration (log axis). Extrapolate the curve down to about 1.0 x 10-5 M or 1 ppm. A typical calibration curve can be found in Figure 1. Figure 1 Typical Chloride Electrode Calibration Curve 0 electrode potential (mv) ~ 56 mv 10-fold change (ppm) Cl - Concentration (M) A calibration curve is constructed on semi-logarithmic paper when using a ph/mv meter in the millivolt mode. The measured electrode potential in mv (linear axis) is plotted against the standard concentration (log axis). In the linear region of the curve, only three standards are necessary to determine a calibration curve. In the non-linear region, additional points must be measured. The direct measurement procedures given are for the linear portion of the curve. The non-linear portion of the curve requires the use of low level procedures. 7

8 6. To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring. Place the electrode tip in the solution. When the reading has stabilized, record the mv reading. Determine the concentration directly from the calibration curve. 7. The calibration should be checked every two hours. Assuming no change in ambient temperature, place the electrode tip in the mid-range standard. After the reading has stabilized, compare it to the original reading recorded in Step 3 above. A reading differing by more than 0.5 mv or a change in the ambient temperature will necessitate the repetition of Step 2-5 above. A new calibration curve should be prepared daily. Direct Measurement of Chloride (using a ion meter) 1. By serial dilution of the 0.1M or 1000 ppm chloride standard, prepare two chloride standards whose concentration is near the expected sample concentration. Measure out 100 ml of each standard into individual 150 ml beakers and add 2 ml of ISA to each. 2. Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate. Assure that the meter is in the concentration mode. 3. Lower the electrode tip into the solution. 4. Adjust the meter to the concentration of the chloride standard and fix the value in the memory according to the meter manufacturer s instructions after stabilization of the reading. 5. Rinse the electrode with distilled water and blot dry. 6. Place the more concentrated solution on the magnetic stirrer and begin stirring at a constant rate. 7. Lower the electrode tip into the solution. 8. Adjust the meter to the concentration of the chloride standard and fix the value in the memory according to the meter manufacturer s instructions after stabilization of the reading. 9. For low level measurements, place the rinsed, dried electrodes into the solution containing 100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank value in the meter according to the meter manufacturer s instructions. 10. Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker, place it on the magnetic stirrer, and begin stirring. 8

9 11. Immerse the electrode tip in the solution and wait for the reading to stabilize. Read the concentration directly from the meter display. 12. The calibration should be checked every two hours. Assuming no change in ambient temperature, place the electrode tip in the first chloride standard. After the reading has stabilized, compare it to the original reading in Step 4 above. A reading differing by more than 0.5 mv or a change in the ambient temperature will necessitate the repetition of Steps 2-8(9) above. The meter should be recalibrated daily. Low Level Chloride Determination (using a ph/mv meter) Use the following low level chloride measurement procedure in the non-linear portion of the calibration curve. (See Figure 1). This procedure is recommended for solutions containing less than 1.0 x 10-4 M. 1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level ISA (1.0M NaNO 3 ) is added at the rate of 1 ml low level ISA to each 100 ml of sample. The background ionic strength will be 1.0 X 10-2 M. 2. Dilute 10 ml of 0.1M standard to 100 ml to prepare a 1.0 x 10-2 M standard solution for measurements in moles per liter. Use the 1000 ppm standard for measurements in ppm. Standards should be prepared fresh daily. 3. Add 1 ml of the low level ISA to a 100 ml volumetric flask and fill to the mark with distilled water. Pour this solution into a 150 ml beaker and place the beaker on the magnetic stirrer. Begin stirring at a constant rate. 4. Place the electrode tip in the solution. Assure that the meter is in the mv mode. 5. Add increments of the 1.0 x 10-2 M or 1000 ppm standard as given in Table 2 below. 6. After the reading has stabilized, record the mv reading after each addition. 9

10 TABLE 2: Step-wise Calibration for Low Level Chloride Measurements Added Concentration Step Pipet Volume (ml) Molarity ppm 1 A x A x A x A x A x B x B x Pipet A = 1 ml graduated pipet Pipet B = 2 ml pipet Solutions: additions of 1000 ppm or 1.0 x 10-2 M standard to 100 ml of ISA as prepared in Step 3 above. 7. On semi-logarithmic graph paper, plot the millivolt reading (linear axis) against the concentration (log axis) as in Figure Rinse the electrode in distilled water and blot dry. 9. Measure out 100 ml of the sample into a 150 ml beaker, add 1 ml of low level ISA, and place the beaker on the magnetic stirrer. Begin stirring. Lower the electrode tip into the solution. After the reading has stabilized, record the mv reading and determine the concentration from the low level calibration curve. 10. Prepare a new low level calibration curve daily. Check the calibration curve every two hours by repeating Steps 2-7. Low Level Chloride Determination (using an ion meter) Follow the procedure given for normal chloride determinations using an ion meter and the blank correction procedure. ELECTRODE CHARACTERISTICS Reproducibility Electrode measurements reproducible to +2% can be obtained if the electrode is calibrated every hour. Factors such as temperature fluctuations, drift, and noise limit reproducibility. Reproducibility is independent of concentration within the electrode s operating range. 10

11 Interferences A surface layer of silver metal may be formed by strongly reducing solutions. A layer of silver salt may be deposited on the membrane if high levels of ions forming very insoluble salts are present in the sample. Performance may be restored by polishing. See the section Electrode Response for proper polishing procedure. Though measurements can be made in solutions containing oxidizing agents such as MnO 4-1, mercury ions must not be present in the samples. The maximum allowable ratio of interfering ion to chloride ion is given in Table 3. This ratio is expressed as the ratio of the interfering ion molarity to the chloride molarity. Readings will be in error if this ratio is exceeded. Neither accuracy of the measurement nor surface of the electrode membrane will be affected if the ratio is less than that listed in the table. TABLE 3: Maximum Allowable Ratio of Interfering Ion to Chloride Ion Interferences Interfering Ion (M) / Chloride Ion (M) OH -1(1) 80 (2) NH x (2) S 2 O x 10-2 Br -1 (3) 3.0 x 10-3 S -2 (4) 1.0 x 10-6 I -1 (3) 5.0 x 10-7 CN -1 (4) 2.0 x Acidify with 1M HNO 3 to ph 4 to remove hydroxide interference. 2. These substances represent complexing species whose maximum level can be exceeded without electrode damage. Value shown represents a 1% error. 3. Add CISA to solutions containing mixed halides to remove interferences. See the procedure below. 4. Add CISA or a solution of Ni +2 to remove sulfide or cyanide interferences. Removal of Various Interferences with CISA CISA is an oxidizing agent which will oxidize up to a 100-fold excess of CN -1 over Cl -1, 100 ppm NH 3, 100 ppm Br -1 or I -1, or 500 ppm S -2. Chloride measurement interferences may be removed by using CISA. The reagents used to prepare CISA are strong oxidizing agents and should be handled in a fume hood. 11

12 To prepare CISA, add approximately 800 ml of distilled water to a 1 liter volumetric flask. Add 15.1 grams of NaBrO 3 to the flask and swirl to dissolve the solid. Slowly add 75 ml of concentrated nitric acid (70% w/w or 15.9N), mix, and dilute to the mark with distilled water. To use CISA, mix equal amounts of CISA and sample. Solutions should be allowed to stand for ten minutes before measuring. Since chloride will be oxidized upon prolonged standing, all standards or samples mixed with CISA should be discarded after measuring. A fresh mixture of CISA and standard should be prepared for each calibration. After adding CISA, follow the procedures for direct measurement. Complexation Total concentration (C t ) consists of free ions (C f ) and complexed or bound ions (C c ) in solution: C t = C f + C c Since the electrode only responds to free ions, any complexing agent in the solution reduces the measured concentration of ions. Chloride ions complex with some metal ions. Table 4 lists the levels of complexing metals causing a 10% error at 1.0 x 10-4 M chloride. TABLE 4: Levels of Complexing Agents Causing a 10% Error at 1.0 x 10-4 M Chloride Ion Concentration Bi +3 Cd +2 Mn +2 Pb +2 Sn +2 Tl x 10-4 M (80 ppm) 2.0 x 10-3 M (200 ppm) 2.0 x 10-2 M (1100 ppm) 2.0 x 10-3 M (400 ppm) 6.0 x 10-3 M (700 ppm) 4.0 x 10-5 M (8 ppm) Temperature Influences Samples and standards should be within ±1 C of each other, since electrode potentials are influenced by changes in temperature. Because of the solubility equilibria on which the electrode depends, the absolute potential of the reference electrode changes slowly with temperature. The slope of the electrode, as indicated by the factor S in the Nernst equation, also varies with temperature. Table 5 gives values for the S factor in the Nernst equation for the chloride ion. 12

13 TABLE 5: Temperature vs. Values for the Electrode Slope Temp. ( C) S If changes in temperature occur, the electrodes should be re-calibrated. The temperature range for the Cole-Parmer Chloride Ion Electrodes is 0-80 C, provided that temperature equilibrium has occurred. If the temperature varies substantially from room temperature, equilibrium times up to one hour are recommended. Electrode Response Plotting the electrode mv potential against the chloride concentration on semi-logarithmic paper results in a straight line with a slope of about 56 mv per decade. (Refer to Figure 1.) The time needed to reach 99% of the stable electrode potential reading, the electrode response time, varies from several seconds in highly concentrated solutions to several minutes near the detection limit. (Refer to Figure 2.) + 50 Figure 2 Typical Electrode Time Response to Step Changes in NaCl 10-3 M to 10-2 M NaCl electrode potential (mv) M to 10-4 M NaCl M to 10-5 M NaCl 1 2 Time (minutes)

14 A drifting potential reading or a decrease in electrode slope may mean that the electrode membrane needs polishing. To polish the membrane: 1. If using polishing paper, cut off a 1-2" piece and place it face up on the lab bench. 2. Put a few drops of distilled or deionized water in the center of the paper. 3. Holding the paper (cotton) steady with one hand, bring the membrane of the electrode down perpendicular to the paper and, with a slight swirling motion, gently polish the tip of the electrode against the surface of the polishing paper (cotton) for a few seconds. 4. Rinse the electrode surface with distilled or deionized water and soak the electrode tip in standard solution for about five minutes before use. 5. If using jeweller s rouge, place a cotton ball on the table top and flatten it using the bottom of a beaker. 6. Put 1-2 drops of distilled or deionized water in the center of the cotton pad. 7. Add a small amount of jeweller s rouge to the damp cotton. 8. Continue with Steps 3 and 4 above. Limits of Detection The upper limit of detection in pure sodium chloride solutions is 1M. In the presence of other ions, the upper limit of detection is above 1.0 x 10-1 M chloride, but two factors influence this upper limit. Both the possibility of a liquid junction potential developing at the reference electrode and the salt extraction effect influence this upper limit. Some salts may extract into the electrode membrane at high salt concentrations, causing deviation from the theoretical response. Either dilute samples between 1M and 1.0 x 10-1 M or calibrate the electrode at 4 or 5 intermediate points. The lower limit of detection is influenced by the slight water solubility of the electrode pellet. Refer to Figure 1 for a comparison of the theoretical response to the actual response at low levels of chloride. Chloride measurements below 10-4 M Cl -1 should employ low level procedures. ph Effects Hydroxide ion interferes with measurements of low levels of chloride although the electrode can be used over a reasonable ph range. Table 3 should be used to determine the minimum ph at which low level chloride measurements can be made without more than a 10% error due to hydroxide ion interference. 14

15 Electrode Life The chloride electrode will last six months in normal laboratory use. On-line measurements might shorten operational lifetime to several months. In time, the response time will increase and the calibration slope will decrease to the point calibration is difficult and electrode replacement is required. Electrode Storage The Cole-Parmer Chloride Electrodes may be stored for short periods of time in 1.0 x 10-2 M chloride solution. For longer storage (longer than two weeks), rinse and dry the sensing pellet and cover the membrane tip with any protective cap shipped with the electrode. The reference portion of the combination electrode should be drained of filling solution, if refillable, and the rubber insert placed over the filling hole. ELECTRODE THEORY Electrode Operation The Cole-Parmer Chloride Ion Electrodes are composed of a glass or an epoxy body and a silver chloride/silver sulfide membrane. When the membrane is in contact with a solution containing chloride ions, an electrode potential develops across the membrane. This electrode potential is measured against a constant reference potential, using a ph/mv meter or an ion meter. The level of chloride ions, corresponding to the measured potential, is described by the Nernst equation: E = E o - S logx where: E = measured electrode potential E o = reference potential (a constant) S = electrode slope ( ~ 56 mv/decade) X = level of chloride ions in solution The activity, X, represents the effective concentration of the ions in solution. The activity is related to the free ion concentration, C f, by the activity coefficient, γ, by: X = γ C f Activity coefficients vary, depending on total ionic strength, I, defined as: where: C x Z x Σ 2 I = ½ Σ C x Z x = concentration of ion X = charge of ion X = sum of all of the types of ions in the solution 15

16 In the case of high and constant ionic strength relative to the sensed ion concentration, the activity coefficient, γ, is constant and the activity, X, is directly proportional to the concentration. To adjust the background ionic strength to a high and constant value, ionic strength adjuster (ISA) is added to samples and standards. The recommended ISA for chloride is NaNO 3. Solutions other than this may be used as ionic strength adjusters as long as ions that they contain do not interfere with the electrode s response to chloride ions. Samples with high ionic strength (greater than 0.1M) do not need ISA added and standards for these solutions should be prepared with a composition similar to the samples. The reference electrode must also be considered. When two solutions of different composition are brought into contact with one another, liquid junction potentials arise. Millivolt potentials occur from the inter-diffusion of ions in the two solutions. Electrode charge will be carried unequally across the solution boundary resulting in a potential difference between the two solutions, since ions diffuse at different rates. When making measurements, it is important to remember that this potential be the same when the reference is in the standardizing solution as well as in the sample solution or the change in liquid junction potential will appear as an error in the measured electrode potential. The composition of the liquid junction filling solution in the reference electrode is most important. The speed with which the positive and negative ions in the filling solution diffuse into the sample should be equitransferent. No junction potential can result if the rate at which positive and negative charge carried into the sample is equal. Strongly acidic (ph=0-2) and strongly basic (ph=12-14) solutions are particularly troublesome to measure. The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask their effect on the junction potential with any concentration of an equitransferent salt. One must either calibrate the electrodes in the same ph range as the sample or use a known increment method for ion measurement. TROUBLESHOOTING GUIDE The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn: the meter, the glassware, the electrode, the standards & reagents, the sample, and the technique. Meter The meter may be checked by following the check-out procedure in the instrument instruction manual. Glassware Clean glassware is essential for good measurement. Be sure to wash the glassware well with a mild detergent and rinse very well with distilled or deionized water. Clean glassware will drain without leaving water droplets behind. 16

17 Electrodes The electrodes may be checked by using the procedure found in the sections entitled Electrode Slope Check. 1. Be sure to use distilled or deionized water when following the procedures given in Electrode Slope Check. 2. If the electrode fails to respond as expected, see the sections Measuring Hints and Electrode Response. Repeat the slope check. 3. If the electrode still fail to respond as expected, substitute another chloride ion electrode that is known to be in good working order for the questionable electrode. If the problem persists and you are using an electrode pair, try the same routine with a working reference electrode. 4. If the problem persists, the reagent may be of poor quality, interferences in the sample may be present or the technique may be faulty. (See Standards & Reagents, Sample, and Technique sections below.) 5. If another electrode is not available for test purposes, or if the electrode in use is suspect, review the instruction manual and be sure to: - Clean and rinse the electrode thoroughly. - Prepare the electrode properly. - Use the proper filling solution. - Adjust the ph and the ionic strength of the solution by the use of the proper ISA. - Measure correctly and accurately. - Review TROUBLESHOOTING HINTS. Standards & Reagents Whenever problems arise with the measuring procedure that has been used successfully in the past, be sure to check the standard and reagent solutions. If in doubt about the credibility of any of the solutions, prepare them again. Errors may result from contamination of the ISA, incorrect dilution of standards, poor quality distilled/deionized water, or a simple mathematical miscalculation. Sample Look for possible interferences, complexing agents, or substances which could affect the response or physically damage the sensing electrode (or the reference electrode) if the electrodes work perfectly in the standard, but not in the sample. Try to determine the composition of the samples prior to testing to eliminate a problem before it starts. (See Measuring Hints, Sample Requirements, and Interferences.) 17

18 Technique Be sure that the electrode s limit of detection has not been exceeded. Be sure that the analysis method is clearly understood and is compatible with the sample. Refer to the instruction manual again. Reread GENERAL PREPARATION and ELECTRODE CHARACTERISTICS. If trouble still persists, call Cole-Parmer Instrument Company at and ask for the Technical Services Department. 18

19 TROUBLESHOOTING HINTS Symptom Possible Causes Next Step Out of Range Reading Noisy or Unstable Readings (readings continuously or rapidly changing) Drift (reading slowly changing in one direction) defective meter defective electrode electrode not plugged in properly reference electrode not filled air bubble on membrane electrode not in solution defective meter air bubble on membrane ISA not used meter or stirrer not grounded defective electrode electrode exposed to interferences samples and standards at different temperatures electrode exposed to complexing agents incorrect reference filling solution check meter with shorting strap (see meter instruction manual) check electrode operation unplug electrode and reseat be sure reference electrode is filled remove air bubble by redipping electrode put electrode in solution check meter with shorting strap remove air bubble by redipping electrode use recommended ISA ground meter or stirrer replace electrode soak electrode in chloride standard allow solutions to come to room temperature before measurement check section entitled Complexation use recommended filling solution 19

20 Symptom Possible Causes Next Step Low Slope or No Slope Incorrect Answer (but calibration is good) standards contaminated or incorrectly made ISA not used standard used as ISA electrode exposed to complexing agents air bubble on membrane incorrect scaling of semi-log paper incorrect sign incorrect standards wrong units used complexing agents in sample prepare fresh standards use recommended ISA use ISA check section entitled Complexation remove air bubble by redipping electrode plot millivolts on the linear axis. On the log axis, be sure concentration numbers within each decade are increasing with increasing concentration be sure to note sign of millivolt number correctly prepare fresh standards apply correct conversion factor: 10-3 M = 35.5 ppm as Cl -1 check section entitled Complexation 20

21 ELECTRODE SPECIFICATIONS Concentration Range 1M to 5.0 x 10-5 M 35,500 to 1.8 ppm) ph Range 2 to 12 Temperature Range Resistance 0-80 C <1 Mohm Reproducibility ± 2% Samples Size Storage aqueous solutions only; no organic solvents 110 mm length 12 mm diameter 1 m cable length Store in chloride solution ORDERING INFORMATION P/N DESCRIPTION Chloride Ion Electrode, combination, glass body Chloride Ion Electrode, combination, epoxy body Chloride Standard, 0.1M NaCl Chloride Standard, 1000 ppm NaCl Chloride Ionic Strength Adjuster (ISA), 5 M NaNO Reference Electrode Filling Solution, 1M KNO 3, for both the and electrodes ISE Solution Kit. Contains (1) bottle of 1000 ppm Chloride Standard, (1) bottle of ISA, (1) bottle of Reference Filling Solution, (1) Polishing Strip, and (1) Syringe 21